In recent years, components that are made of an aluminum alloy have become more and more in use because weight reduction is required in transportation equipment and the like. Aluminum panels for an automobile and the like are not suitable for welding, and therefore are typically connected using self-piercing rivets.
One example of a self-piercing rivet setting apparatus is described in Japanese Patent Laid-Open Publication No. Hei 8-505087. The self-piercing rivet comprises a large-diameter head and a hollow leg extending downward from the head. When the self-piercing rivet is driven into workpieces, such as two body panels, by a punch and a die of the setting apparatus, the leg of the rivet is driven to pierce the workpieces while allowing the front end of the leg to be expandingly deformed, so as to connect the workpieces with one another by the deformed leg and the head.
Since the self-piercing rivet is driven to allow it to pass through a punch-side workpiece but to stay in a receiving-side workpiece adjacent to the die without passing therethrough, the rivet does not form any penetrating hole in the surface of the receiving-side workpiece. This provides an advantage of maintaining a sealing performance and good appearance of the receiving-side workpiece.
FIG. 1 shows a sectional view of the connecting portion of the workpieces connected by the conventional self-piercing rivet. The self-piercing rivet 1 comprises the large-diameter head 5 and the hollow leg 6 extending downward from the head. The self-piercing rivet 1 is driven into two workpieces 2 and 3 by the punch and the die (not shown) of the setting apparatus. At that time, the leg 6 of the rivet is driven to pierce the workpieces (such as the body panels) while allowing the front end of the leg 6 to be expandingly deformed, so as to connect the punch-side workpiece 2 and the receiving-side workpiece 3 by the deformed leg 6 and the large-diameter head 5.
In this conventional self-piercing-rivet driving operation, however, if the punch-side workpiece is thick and the receiving-side workpiece adjacent to the die is thin, then the leg of the rivet does not penetrate into the receiving-side workpiece adjacent to the die and consequently it is unable to provide a sufficient strength for the connection.
Also, in the conventional self-piercing-rivet driving operation, if more than two workpieces are to be connected, then the leg of the rivet does not penetrate sufficiently through the receiving-side workpiece adjacent to the die, and thereby it is difficult to reliably connect the workpieces together.
The present invention is directed to solve these problems, and therefore it is an object of the present invention to provide a setting apparatus capable of connecting workpieces by a self-piercing rivet, and a die for use in the apparatus, to achieve a sufficient connecting force.
Particularly, in the case of the receiving-side workpiece adjacent to the die is thin, it is also the object of the present invention to provide a setting apparatus capable of reliably connecting workpieces even in the case when more than two workpieces are connected, and a die for use in the apparatus.